Centrifugal pump assemblies having an axial flux electric motor and methods of assembly thereof

ABSTRACT

An electric motor assembly for pumping a fluid through a fluid cavity includes a stator assembly including a plurality of conduction coils configured to transmit heat energy to the fluid within the fluid cavity and a rotor assembly positioned adjacent the stator assembly to define an axial gap therebetween. The stator assembly is configured to impart a first axial force on the rotor assembly. The electric motor assembly also includes an impeller directly coupled to the rotor assembly opposite the stator assembly such that the rotor assembly and the impeller are configured to rotate about an axis. A fluid channeled by the impeller imparts a second axial force on the impeller. The rotor assembly and the impeller are configured to be submerged in the fluid within the fluid cavity.

BACKGROUND

The field of the disclosure relates generally to centrifugal pumpassemblies, and more specifically, to centrifugal pump assemblies thatinclude an axial flux electric motor coupled to an impeller.

At least some known centrifugal pumps include an impeller for channelinga fluid through the pump. The impeller is coupled to a shaft that isalso coupled to a rotor of an electric motor such that rotation of therotor causes rotation of the impeller. In at least some known electricmotors, the rotor is spaced from a stator such that there is an everpresent axial force of attraction between the magnets on the rotor andthe steel core of the stator. The axial force may be large enough suchthat the bearing system of the motor requires special designconsiderations to withstand this axial force. Additionally, the rotatingimpeller imparts kinetic energy into the pumped fluid as it spins, whichincreases the pressure of the fluid. There is a resulting axial suctionforce acting on the impeller as this pressure increases. In at leastsome known centrifugal pumps, the axial suction force may also requirebearing system design considerations.

Furthermore, at least some known centrifugal pumps are located inenvironments that may cause the fluid being channeled therethrough tofreeze when the pump is non-operational. When the fluid freezes, theimpeller may be locked in place and subsequent attempts to rotate theimpeller before defrosting the fluid may result in a shortened servicelifetime of the impeller or the entire pump. Additionally, in at leastsome centrifugal pumps, the stator of the electric motor generates arelatively high amount of heat and may require a complex and high costcooling system.

BRIEF DESCRIPTION

In one aspect, an electric motor assembly is provided. The electricmotor assembly includes a stator assembly and a rotor assemblypositioned adjacent the stator assembly to define an axial gaptherebetween. The stator assembly is configured to impart a first axialforce on the rotor assembly. The electric motor assembly also includesan impeller directly coupled to the rotor assembly opposite the statorassembly such that the rotor assembly and the impeller are configured torotate about an axis. A fluid channeled by the impeller imparts a secondaxial force on the impeller.

In another aspect, a pump assembly is provided. The pump assemblyincludes a pump housing and a motor housing coupled to the pump housing.The pump assembly also includes an electric motor assembly including astator assembly and a rotor assembly positioned adjacent the statorassembly to define an axial gap therebetween. The stator assembly isconfigured to impart a first axial force on the rotor assembly. Theelectric motor assembly also includes an impeller directly coupled tothe rotor assembly opposite the stator assembly such that the rotorassembly and the impeller are configured to rotate about an axis. Afluid channeled by the impeller imparts a second axial force on theimpeller.

In yet another aspect, a method of assembling a pump assembly isprovided. The method includes providing a stator assembly and coupling arotor assembly to the stator assembly such that an axial gap is definedtherebetween. The stator assembly is configured to impart a first axialforce on the rotor assembly. The method also includes coupling animpeller directly to the rotor assembly opposite the stator assemblysuch that the rotor assembly and the impeller are configured to rotateabout an axis. A fluid channeled by the impeller is configured to imparta second axial force on the impeller.

In one aspect, an electric motor assembly for pumping a fluid through afluid cavity is provided. The electric motor assembly includes a statorassembly including a plurality of conduction coils configured totransmit heat energy to the fluid within the fluid cavity. The electricmotor assembly also includes a rotor assembly positioned adjacent thestator assembly to define an axial gap therebetween. The electric motorassembly also includes an impeller directly coupled to the rotorassembly opposite the stator assembly such that the rotor assembly andthe impeller are configured to rotate about an axis. The rotor assemblyand the impeller are configured to be submerged in the fluid within thefluid cavity.

In another aspect, a pump assembly is provided. The pump assemblyincludes a pump housing that defines a fluid cavity and a motor housingcoupled to the pump housing. The pump assembly also includes an electricmotor assembly including a stator assembly positioned within the motorhousing and including a plurality of conduction coils configured totransmit heat energy to the fluid within the fluid cavity. The electricmotor assembly also includes a rotor assembly positioned adjacent thestator assembly and within the pump housing. The electric motor assemblyalso includes an impeller directly coupled to the rotor assemblyopposite the stator assembly such that the rotor assembly and theimpeller are configured to rotate about an axis. The rotor assembly andthe impeller are configured to be submerged in the fluid within thefluid cavity.

In yet another aspect, a method of assembling a pump assembly forpumping a fluid through a fluid cavity is provided. The method includesproviding a stator assembly including a plurality of conduction coilsthat are configured to transmit heat energy to the fluid within thefluid cavity. The method also includes positioning a rotor assemblyadjacent the stator assembly such that an axial gap is definedtherebetween and coupling an impeller directly to the rotor assemblyopposite the stator assembly such that the rotor assembly and theimpeller are configured to rotate about an axis. The rotor assembly andthe impeller are configured to be submerged in the fluid within thefluid cavity.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an exemplary centrifugal pump;

FIG. 2 is a cross-sectional view of the centrifugal pump shown in FIG.1;

FIG. 3 is an enlarged cross-sectional view of the centrifugal pump shownin FIG. 2 illustrating an electric motor and an impeller;

FIG. 4 is a perspective view of an alternative embodiment of acentrifugal pump;

FIG. 5 is a bottom perspective view of the centrifugal pump shown inFIG. 4 illustrating an impeller;

FIG. 6 is a cross-sectional view of the centrifugal pump shown in FIG. 4illustrating the impeller and an electric motor; and

FIG. 7 is an enlarged cross-sectional view of a portion of the electricmotor and the impeller bounded by box 7-7 in FIG. 6.

Although specific features of various embodiments may be shown in somedrawings and not in others, this is for convenience only. Any feature ofany drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

DETAILED DESCRIPTION

FIG. 1 is a perspective view of an exemplary centrifugal pump assembly100. FIG. 2 is a cross-sectional view of pump assembly 100 illustratingan axial flux electric motor assembly 102, an impeller 104, and a pumphousing 106. FIG. 3 is an enlarged cross-sectional view of electricmotor assembly 102 and impeller 104 with pump housing 106 removed forclarity. In the exemplary embodiment, pump assembly 100 includes pumphousing 106 and a motor housing 108. Pump housing 106 encloses impeller104 and at least a portion of motor assembly 102, while motor housing108 encloses motor assembly 102. Pump housing 106 includes a fluid inlet110, a scroll wall 112 defining a portion of a fluid flow channel 114,and a fluid outlet 116. In operation, fluid flows through inlet 110 andis directed through channel 114 around wall 112 until the fluid exitspump 100 through housing outlet 116.

In the exemplary embodiment, impeller 104 is positioned within pumphousing 106 and includes an inlet ring 118 that defines an inlet opening120. Impeller 104 also includes a rear plate 122 and a plurality ofblades 124 coupled between inlet ring 118 and rear plate 122. Asdescribed in further detail herein, rear plate 122 of impeller 102 iscoupled directly to motor assembly 102 such that motor assembly 102 isconfigured to rotate impeller 102 about a rotational axis 126. Inoperation, motor 102 rotates impeller 104 about axis 126 to draw fluidin an axial direction into pump housing 106 through housing inlet 110.The fluid is channeled through inlet opening 120 in inlet ring 118 andturned by blades 124 within channel 114 to direct the fluid along wall112 and radially through housing outlet 116. The amount of fluid movedby pump assembly 100 increases as impeller 104 speed increases such thatimpeller 104 generates high velocity fluid flow that is exhausted fromoutlet 116.

Impeller 104 imparts kinetic energy into the pumped fluid as it rotatesthat causes the fluid to pressurize. In the exemplary embodiment, thepressurized fluid imparts an axial suction force 128 on impeller 104.Axial force 128 acts in an axial direction away from motor assembly 102through pump housing inlet 110. As the speed of impeller 104 increases,both the pressure of the fluid and the resulting axial suction force 128also increase correspondingly. That it, the magnitude of axial suctionforce 128 is based on the rotational speed of impeller 104.

In the exemplary embodiment, motor assembly 102 includes motor housing108 including a first portion 130 and a second portion 132. Motorassembly 102 also includes a stator assembly 133 including a magneticstator core 134 and a plurality of conductor coils 136. Motor assembly102 also includes a bearing assembly 138 and a rotor assembly 140. Eachconductor coil 136 includes an opening (not shown) that closely conformsto an external shape of one of a plurality of stator core teeth 142 suchthat each stator tooth 142 is configured to be positioned within aconductor coil 136. Motor assembly 102 may include one conductor coil136 per stator tooth 142 or one conductor coil 136 positioned on everyother tooth 142. Stator core 134 and coils 136 are positioned withinsecond portion 132 of motor housing 108, which is coupled to pumphousing 106 with a plurality of fasteners 144.

In the exemplary embodiment, a variable frequency drive (not shown)provides a signal, for example, a pulse width modulated (PWM) signal, tomotor 102. In an alternative embodiment, motor 102 may include acontroller (not shown) coupled to conductor coils 136 by wiring. Thecontroller is configured to apply a voltage to one or more of conductorcoils 136 at a time for commutating conductor coils 136 in a preselectedsequence to rotate rotor assembly 140 about axis 126.

Rotor assembly 140 is positioned within pump housing 106 proximatechannel 114 and includes a back iron or rotor disk 146 having at least afirst axial surface 148. Rotor assembly 140 also includes a magnetretainer 150 coupled to rotor disk 146 opposite impeller 104 and aplurality of permanent magnets 152 coupled to magnet retainer 150 usingan adhesive. Alternatively, magnets 152 may be coupled to magnetretainer 150 using any retention method that facilitates operation ofmotor 102 as described herein. In another embodiment, magnets 152 arecoupled directly to rotor disk 146.

In the exemplary embodiment, rotor assembly 140 is positioned adjacentstator assembly 133 to define an axial gap 154 therebetween. Asdescribed above, voltage is applied to coils 136 in sequence to causerotation of rotor assembly 140. More specifically, coils 136 control theflow of magnetic flux between magnetic stator core 134 and permanentmagnets 152. Magnets 152 are attracted to magnetic stator core 134 suchthat an axial magnetic force 156 is ever-present across gap 154. Assuch, stator core 134 of stator assembly 133 imparts axial magneticforce 156 to rotor assembly 140 in an axial direction away from impeller104. More specifically, axial magnetic force 156 acts in a directionopposite of axial suction force 128 of impeller 104. As the size ofaxial gap 154 decreases, the axial magnetic force 156 between statorassembly 133 and rotor assembly 140 increases. That is, the magnitude ofaxial magnetic force 156 is based on a length of axial gap 154.

Rotor disk 146 is coupled to a rotating component 158 of bearingassembly 138 and stator assembly 133 is coupled to a stationarycomponent 160 of bearing assembly 138. In the exemplary embodiment,bearing assembly 138 includes a hydrodynamic bearing wherein rotatingcomponent 158 is coupled to rotor disk 146 using a plurality offasteners 162. In other embodiments, bearing assembly 138 includes anybearing type that facilitates operation of motor 102 as describedherein.

As best shown in FIG. 3, impeller 104 is directly coupled to rotorassembly 140 opposite stator assembly 133 such that impeller 104contacts rotor assembly 140 to enable rotation of impeller 104 and rotorassembly 140 about axis 126. As used herein, the term “directly” ismeant to describe that rotor assembly 140 is coupled to impeller 104without any intermediate structure positioned therebetween to separaterotor assembly 140 from impeller 104. More specifically, rotor disk 146is directly coupled to impeller 104. Even more specifically, rotor disk146 is directly coupled to rear plate 122 of impeller 104. In oneembodiment, axial surface 148 of rotor disk 146 is coupled to anddirectly contacts an axial surface 164 of rear plate 122 in aface-to-face relationship. In the exemplary embodiment, and as shown inFIG. 3, rotor disk 146 is coupled to impeller back plate 122 using aplurality of fasteners 166. In another embodiment, rotor assembly 140 isintegrally formed with impeller 104. More specifically, rotor disk 146is integrally formed with rear plate 122 of impeller 104 such that rotordisk 146 and rear plate 122 form a single, monolithic component.Generally, rotor assembly 140 and impeller 104 are directly coupledtogether using any attachment means that facilitates operation of pumpassembly 100 as described herein. As described above, conventional pumpsinclude a shaft that couples the rotor assembly to the impeller.However, in one embodiment described herein, as shown in FIGS. 2 and 3,pump assembly 100 does not include a shaft coupled between rotorassembly 140 and impeller 104 as impeller 104 is directly coupled to andcontacting rotor assembly 140.

In operation, conductor coils 136 coupled to stator core 134 areenergized in a chronological sequence that provides an axial magneticfield which moves clockwise or counterclockwise around stator core 134depending on the pre-determined sequence or order in which conductorcoils 136 are energized. This moving magnetic field intersects with theflux field created by the plurality of permanent magnets 152 to causerotor assembly 140 to rotate about axis 126 relative to stator assembly133 in the desired direction. As described above, the magneticattraction between stator core 134 and magnets 152 creates axialmagnetic force 156 that acts in a direction away from impeller 104.Furthermore, because rotor disk 146 is directly coupled to impeller 104,rotation of rotor disk 146 causes rotation of impeller 104. As describedabove, rotation of impeller 104 pressurizes the fluid flowingtherethrough, which imparts axial suction force 128 on impeller 104 in adirection away from rotor assembly 140. As shown in FIG. 3, axialsuction force 128 acts in an opposite direction of axial magnetic force156. In the embodiment, when rotor disk 146 is coupled directly toimpeller 104, axial magnetic force 156 opposes axial suction force 128to reduce the sum of the forces, which facilitates extending the servicelifetime of bearing assembly 138. In some embodiments, forces 156 and128 are equal such that they cancel each other out.

Furthermore, in the exemplary embodiment, axial gap 154 is adjustable tomodify the magnitude of axial magnetic force 156. Additionally, motorassembly 102 is a variable speed motor, so the speed of impeller 104 canalso be adjusted to adjust the axial suction force 128 of the fluid.Modifying at least one of air gap 154 and the speed of impeller 104facilitates creating a desires bias within pump assembly 100 eithertowards motor assembly 102 or towards pump 106. So by reducing theresultant force within pump assembly 100 and by biasing the resultantforce to towards motor assembly 102 or towards pump 106, it is possibleto use a simple and low cost bearing assembly 138 for the integratedpump assembly 100.

FIG. 4 is a perspective view of an alternative embodiment of acentrifugal pump assembly 200 illustrating a pump housing 206 and amotor housing 208. FIG. 5 is a bottom perspective view of centrifugalpump assembly 200 with pump housing 206 removed for clarity andillustrating an impeller 204. FIG. 6 is a cross-sectional view of pumpassembly 200 illustrating impeller 204 and an axial flux electric motorassembly 202, and FIG. 7 is an enlarged cross-sectional view of aportion of electric motor assembly 202 and impeller 204 bounded by box7-7 in FIG. 6.

In the exemplary embodiment, pump assembly 200 includes a pump housing206 and a motor housing 208. Pump housing 206 encloses impeller 204 andat least a portion of motor assembly 202, while motor housing 208encloses motor assembly 202. Pump housing 206 includes a fluid inlet210, a scroll wall 212 defining a portion of a fluid flow channel 214,and a fluid outlet 216. In operation, fluid flows through inlet 210 andis directed through channel 214 around wall 212 until the fluid existspump 200 through housing outlet 216.

In the exemplary embodiment, impeller 204 is positioned within pumphousing 206 and includes an inlet ring 218 that defines an inlet opening220. Impeller 204 also includes a rear plate 222 and a plurality ofblades 224 coupled between inlet ring 218 and rear plate 222. Asdescribed in further detail herein, rear plate 222 of impeller 202 iscoupled directly to motor 202 such that motor 202 is configured torotate impeller 202 about a rotational axis 226. In operation, motor 202rotates impeller 204 about axis 226 to draw fluid in an axial directioninto a fluid cavity 228, defined by pump housing 206, through housinginlet 210. The fluid is channeled through inlet opening 220 in inletring 218 and turned by blades 224 within channel 214 to direct the fluidalong wall 212 within cavity 228 and through housing outlet 216. Theamount of fluid moved by pump assembly 200 increases as impeller 204speed increases such that impeller 204 generates high velocity fluidflow that is exhausted from outlet 216.

In the exemplary embodiment, motor assembly 202 includes a statorassembly 232 including a magnetic stator core 234 and a plurality ofconductor coils 236. Motor assembly 202 also includes a bearing assembly238 and a rotor assembly 240. Each conductor coil 236 includes anopening (not shown) that closely conforms to an external shape of one ofa plurality of stator core teeth 242 such that each stator tooth 242 isconfigured to be positioned within a conductor coil 236. Motor assembly202 may include one conductor coil 236 per stator tooth 242 or oneconductor coil 236 positioned on every other tooth 242.

In the exemplary embodiment, motor assembly 202 also includes anelectronics module 244 that controls operation of motor assembly 202. Inone embodiment, electronics module 244 is coupled to conductor coils 236by wiring and is configured to apply a voltage to one or more ofconductor coils 236 at a time for commutating conductor coils 236 in apreselected sequence to rotate rotor assembly 240 about axis 226. Asshown in FIG. 6, electronics module 244 is coupled to stator assembly232 and positioned, along with stator assembly 232, within a cavity 245defined by motor housing 208.

Rotor assembly 240 is positioned within fluid cavity 228 of pump housing206 and includes a back iron or rotor disk 246 having at least a firstaxial surface 248 (shown in FIG. 7). In the exemplary embodiment, rotorassembly 240 also includes at least one permanent magnet 250 coupled torotor disk 246 opposite impeller 204 using an adhesive. Alternatively,magnet 250 may be coupled to rotor disk 246 using any retention methodthat facilitates operation of motor assembly 202 as described herein. Inanother embodiment, magnet 250 is coupled to a magnet retainer, which isthen coupled to rotor disk 246. Furthermore, magnet 250 is one of asingle, ring-shaped magnet or a plurality of magnets.

In the exemplary embodiment, rotor assembly 240 is positioned adjacentstator assembly 232 to define an axial gap 254 (shown in FIG. 7)therebetween. Furthermore, impeller 204 is directly coupled to rotorassembly 240 opposite stator assembly 232 such that impeller 204 androtor assembly 240 rotate about axis 226 and are positioned within fluidcavity 228 and are submerged in the fluid within fluid cavity 228. Morespecifically, rotor disk 246 is coupled to impeller 204. Even morespecifically, rotor disk 246 is coupled to rear plate 222 of impeller204. In one embodiment, axial surface 248 of rotor disk 246 is coupledto an axial surface 255 of rear plate 222 in a face-to-facerelationship. In the exemplary embodiment, and as shown in FIG. 7, rotordisk 246 is coupled to impeller back plate 222 using a plurality offasteners 257. In another embodiment, rotor assembly 240 is integrallyformed with impeller 204. More specifically, rotor disk 246 isintegrally formed with rear plate 222 of impeller 204. Generally, rotorassembly 240 and impeller 204 are directly coupled together using anyattachment means that facilitates operation of pump assembly 200 asdescribed herein.

In the exemplary embodiment, impeller 204 includes a cylindricalextension 256 that extends axially from rear plate 222 towards motorhousing 208. Extension 256 is coupled to a rotating component 258 ofbearing assembly 238. Rotating component 258 circumscribes a stationarycomponent 260 of bearing assembly 238. In the exemplary embodiment,bearing assembly 238 includes a hydrodynamic bearing. In otherembodiments, bearing assembly 238 includes any bearing type thatfacilitates operation of motor 102 as described herein.

As best shown in FIG. 7, motor housing 208 also includes a wall 262 thatseparates fluid cavity 228 from stator assembly 232 and that at leastpartially defines cavity 245. More specifically, wall 262 limits theflow of the fluid to within pump housing 206 and substantially sealsstator assembly 232 and electronics module 244 from fluid cavity 228. Inthe exemplary embodiment, wall 262 includes an axial portion 264positioned immediately radially inward of conductor coils 236 such thata radial gap 266 is formed between wall axial portion 264 and impellerextension 256. As described herein, gap 266 enables fluid flow betweenwall 262 of motor housing 208 and extension 256 of impeller 204.Furthermore, wall 262 also includes a radial portion 268 extendingradially within axial gap 254 between stator assembly 232 and rotorassembly 240. Additionally, wall 262 defines a fluid channel 270 that isin fluid communication with fluid cavity 228 radially outward ofconductor coils 236. In the exemplary embodiment, as described infurther detail below, wall portions 264 and 268 form a barrier betweenfluid cavity 228 and motor cavity 245 that houses stator assembly 232and electronics module 244. Wall portions 264 and 268 are positionedproximate conductor coils 236 such that, when heating is desired, heatfrom conductor coils 236 is transmitted through wall portions 264 and268 to heat the fluid within fluid cavity 228. Similarly, duringoperation, the relatively cool fluid flowing passed wall 262 acts tocool conductor coils 236 and stator core 234 of stator assembly 232 andalso to cool electronics module 244.

In operation, electronics module 244 is configured to apply a voltage toone or more of conductor coils 236 at a time for commutating conductorcoils 236 in a preselected sequence to rotate rotor assembly 240 aboutaxis 226. Conductor coils 236 coupled to stator core 234 are energizedin a chronological sequence that provides an axial magnetic field whichmoves clockwise or counterclockwise around stator core 234 depending onthe pre-determined sequence or order in which conductor coils 236 areenergized. This moving magnetic field intersects with the flux fieldcreated by permanent magnets 250 to cause rotor assembly 240 to rotateabout axis 226 relative to stator assembly 232 in the desired direction.

In the exemplary embodiment, the voltage applied to conductor coils 236can be controlled such that the electrical energy within conductor coils236 is converted to heat energy 272 that radiates from coils 236.Furthermore, a frequency is applied to conductor coils 236 to change themagnetic flux in rotor assembly 240 such that electromagnetic parts ofrotor assembly 240, i.e. rotor disk 246 are heated. Heat energy 272radiates from conductor coils 236 and is transmitted to the fluid withinfluid cavity 228. More specifically, heat energy 272 is transmitted fromconductor coils 236 and through axial portion 264 and radial portion 268of wall 262 to the fluid within fluid cavity 228. Furthermore, becauserotor assembly 240 is positioned proximate stator assembly 232, heatenergy 272 also facilitates heating magnet 250 and/or rotor disk 246such that the fluid immediately surrounding magnet 250 and/or rotor disk246 increases in temperature. Induction heating of pump assembly 200 asdescribed herein serves to either prevent the fluid from freezing or todefrost already frozen fluid.

In the exemplary embodiment, the pump assembly 200 may be located in anenvironment that causes the fluid within fluid cavity 228 to freeze whenpump assembly 200 is non-operational. Because rotor assembly 240 andimpeller 204 are submerged in the fluid, when the fluid freezes, rotorassembly 240 and impeller 204 may be locked in place. In such asituation, voltage can be applied in a manner to heat conductor coils236 without causing rotation of rotor assembly 240. Heat energy 272 isthen transmitted through wall 262 to the frozen fluid and to magnet 250and/or rotor disk 246 to facilitate thawing the fluid to enable rotationof submerged rotor assembly 240 and impeller 204. Specifically, heatenergy 272 is transmitted to axial gap 254 and to radial gap 266 tofacilitate heating the fluid therein. Coupling rotor assembly 240 toimpeller 204 and positioning rotor assembly 240 and impeller 204 withinfluid cavity 228 and also in close proximity to conductor coils 236 ofstator assembly 232 enables heat energy 272 to increase the temperatureof the fluid within cavity 272 and also increase the temperature ofmagnet 250 and/or rotor disk 246. Furthermore, submerging rotor assembly240 in the fluid within fluid cavity 228 exposes rotor assembly 240 tothe fluid, which facilitates cooling magnet 250 and/or rotor disk 246and prevents rotor assembly 240 from exceeding a predeterminedtemperature limit.

Additionally, during standard operation, both conductor coils 236 andelectronics module 244 generate heat that may require cooling to preventconductor coils 236 and electronics module 244 from exceeding apredetermined temperature limit. In the exemplary embodiment, conductorcoils 236 and electronics module 244 are positioned with motor housing208 of pump assembly 200 within close proximity of fluid cavity 228. Asdescribed above, the relatively cool fluid flows along axial portion 264and radial portion 268 of wall 262 such that the temperature of wall 262is reduced. The cooled wall 262 reduces the temperature of motor cavity245, which facilitates cooling conductor coils 236 and electronicsmodule 244 within cavity 245. The close proximity of conductor coils 236and electronics module 244 within motor cavity 245 to the fluid withinfluid cavity 228 of pump housing 206 facilitates reducing thetemperature of conductor coils 236 and electronics module 244.

The apparatus, methods, and systems described herein provide a pumpassembly having an electric motor coupled to an impeller. Morespecifically, a rotor assembly of the motor is directly coupled to theimpeller. The rotor assembly is subject to an axial suction force fromthe stator assembly, and the impeller is subject to an axial suctionforce from the fluid flowing therethrough. As described herein, theaxial suction force acts in an opposite direction of the axial magneticforce to reduce the sum of the forces, which facilitates extending theservice lifetime of the motor assembly, and, specifically, the bearingassembly.

Furthermore, directly coupling the rotor assembly and the impeller andpositioning the rotor assembly proximate the stator assembly enablesheat transfer from the stator assembly to the rotor assembly and thefluid within the pump. More specifically, voltage is applied to aplurality of conductor coils of the stator assembly to increase thetemperature of the conductor coils. Heat energy radiates from theconductor coils and is transmitted through a wall of the motor housingto the rotor assembly and to the fluid in which the rotor assembly issubmerged to facilitate increasing the temperature of the fluid and therotor assembly. Additionally, submerging the rotor assembly in the fluidexposes the rotor assembly to the fluid, which facilitates coolingcomponents of the rotor assembly and prevents the rotor assembly fromoverheating. Furthermore, the close proximity of the conductor coils andthe electronics module within the motor cavity to the fluid within thefluid cavity of the pump housing facilitates cooling the conductor coilsand the electronics module.

Exemplary embodiments of the centrifugal pump assembly are describedabove in detail. The centrifugal pump assembly and its components arenot limited to the specific embodiments described herein, but rather,components of the systems may be utilized independently and separatelyfrom other components described herein. For example, the components mayalso be used in combination with other machine systems, methods, andapparatuses, and are not limited to practice with only the systems andapparatus as described herein. Rather, the exemplary embodiments can beimplemented and utilized in connection with many other applications.

Although specific features of various embodiments of the disclosure maybe shown in some drawings and not in others, this is for convenienceonly. In accordance with the principles of the disclosure, any featureof a drawing may be referenced and/or claimed in combination with anyfeature of any other drawing.

This written description uses examples to disclose the invention,including the best mode, and to enable any person skilled in the art topractice the invention, including making and using any devices orsystems and performing any incorporated methods. The patentable scope ofthe invention is defined by the claims, and may include other examplesthat occur to those skilled in the art. Such other examples are intendedto be within the scope of the claims if they have structural elementsthat do not differ from the literal language of the claims, or if theyinclude equivalent structural elements with insubstantial differencesfrom the literal languages of the claims.

What is claimed is:
 1. An electric motor assembly comprising: a statorassembly; a rotor assembly positioned adjacent said stator assembly todefine an axial gap therebetween, wherein said stator assembly imparts afirst axial force on said rotor assembly; a bearing assembly comprising:a rotating member having a stepped radial portion directly coupled to arotor disk of said rotor assembly opposite said stator assembly, whereinsaid stepped radial portion is aligned with two inner surfaces of therotor disk of said rotor assembly along an axis of rotation; and astationary member positioned radially outward of said rotating member,wherein said rotating member comprises an axial portion positionedwithin an opening of said stationary member, wherein said axial portionis a radially innermost component of said electric motor assembly; andan impeller directly coupled to said rotor assembly opposite said statorassembly such that said rotor assembly and said impeller are configuredto rotate about the axis of rotation, wherein a fluid channeled by saidimpeller imparts a second axial force on said impeller.
 2. The electricmotor assembly in accordance with claim 1, wherein the first axial forceacts on said rotor assembly in a first direction, and wherein the secondaxial force acts on said impeller in a second direction opposite thefirst direction.
 3. The electric motor assembly in accordance with claim1, wherein said rotor assembly further comprises a plurality ofpermanent magnets, wherein said rotor disk is directly coupled to saidimpeller such that rotor disk contacts said impeller.
 4. The electricmotor assembly in accordance with claim 3, wherein said impellercomprises a front plate defining an inlet and an opposing rear plate,said rear plate directly coupled to said rotor disk.
 5. The electricmotor assembly in accordance with claim 1, wherein said impellercomprises a front plate defining an inlet, an opposing rear plate, and aplurality of blades coupled therebetween, wherein said rear plate isdirectly coupled in a face-to-face relationship with said rotorassembly.
 6. The electric motor assembly in accordance with claim 1,further comprising a plurality of fasteners configured to couple saidrotor assembly to said impeller.
 7. The electric motor assembly inaccordance with claim 1, wherein said impeller is integrally formed withsaid rotor assembly.
 8. The electric motor assembly in accordance withclaim 1, wherein said electric motor assembly does not include a shaftcoupled between said rotor assembly and said impeller.
 9. The electricmotor assembly in accordance with claim 1, wherein the axial portion ofsaid rotating member and said impeller do not axially overlap.
 10. Theelectric motor assembly in accordance with claim 1, wherein saidstationary member comprises a radially-oriented flange that is axiallyaligned with at least one permanent magnet of said rotor assembly. 11.The electric motor assembly in accordance with claim 1, wherein saidrotor assembly comprises a cavity configured to receive a rear plate ofsaid impeller.
 12. The electric motor assembly in accordance with claim1, wherein said rotor disk is coupled to said impeller, and wherein saidstepped radial portion of said rotating member is aligned along saidaxis of rotation with said rotor disk.
 13. A pump assembly comprising: apump housing; a motor housing coupled to said pump housing; an electricmotor assembly comprising: a stator assembly; a rotor assemblypositioned adjacent said stator assembly to define an axial gaptherebetween, wherein said stator assembly imparts a first axial forceon said rotor assembly; a bearing assembly comprising a rotating memberhaving a stepped radial portion coupled directly to a rotor disk of saidrotor assembly opposite said stator assembly, wherein said steppedradial portion is aligned with two inner surfaces of the rotor disk ofsaid rotor assembly along an axis of rotation; and a stationary memberpositioned radially outward of said rotating member, wherein saidrotating member comprises an axial portion positioned within an openingof said stationary member, wherein said axial portion is a radiallyinnermost component of said electric motor assembly; and an impellerdirectly coupled to said rotor assembly opposite said stator assemblysuch that said rotor assembly and said impeller are configured to rotateabout the axis of rotation, wherein a fluid channeled by said impellerimparts a second axial force on said impeller.
 14. The pump assembly inaccordance with claim 13, wherein said rotor assembly further comprisesa plurality of permanent magnets, wherein said rotor disk is directlycoupled to said impeller such that said rotor disk contacts saidimpeller.
 15. The pump assembly in accordance with claim 13, whereinsaid impeller comprises a front plate defining an inlet, an opposingrear plate, and a plurality of blades coupled therebetween, wherein saidrear plate is directly coupled in a face-to-face relationship with saidrotor assembly.
 16. The pump assembly in accordance with claim 13,wherein said impeller is integrally formed with said rotor assembly. 17.A method of assembling a pump assembly, said method comprising:providing a stator assembly; magnetically coupling a rotor assembly tothe stator assembly such that an axial gap is defined therebetween,wherein the stator assembly imparts a first axial force on the rotorassembly; coupling a stepped radial portion of a rotating component of abearing assembly directly to the rotor assembly such that the steppedradial portion of the rotating component is aligned with two innersurfaces of the rotor assembly along an axis of rotation; coupling astationary component radially outward of the rotating component, whereinthe rotating component includes an axial portion positioned within anopening of the stationary component, wherein the axial portion is theradially innermost component of the pump assembly; and coupling animpeller directly to the rotor assembly opposite the stator assemblysuch that the rotor assembly and the impeller are configured to rotateabout the axis of rotation, wherein a fluid channeled by the impeller isconfigured to impart a second axial force on the impeller.
 18. Themethod in accordance with claim 17, further comprising: coupling a pumphousing to a motor housing of the pump assembly; coupling the statorassembly within the motor housing; and positioning the rotor assemblyand the impeller within the pump housing.
 19. The method in accordancewith claim 17, further comprising modifying a length of the axial gap tochange the magnitude of the first axial force.
 20. The method inaccordance with claim 17, further comprising modifying a speed of theimpeller to change the magnitude of the second axial force.
 21. Themethod in accordance with claim 17, wherein coupling the impellerdirectly to the rotor assembly comprises coupling a rotor disk of therotor assembly directly to the impeller such that the rotor diskcontacts the impeller.
 22. The method in accordance with claim 17,wherein coupling the impeller directly to the rotor assembly comprisescoupling a rear plate of the impeller in a face-to-face relationshipwith the rotor assembly.
 23. The method in accordance with claim 17,wherein coupling the impeller directly to the rotor assembly comprisesintegrally forming the impeller with the rotor assembly.